a. Field of the Invention
This invention relates to the field of optics and, more particularly, to improvements in instrumentation for use in that field. Still more specifically, this invention pertains to instrumentation adapted for use with what will be referred to as "optical-type" radiations (i.e., infrared, visible and ultraviolet radiations of wavelengths conforming to the laws of optics relating to transmission, reflection and refraction) and concomitantly provides, first, an improved kind of optical masking device having masking characteristics (in terms of transmissivity versus reflectivity and/or opacity) that are selectively and quickly alterable under electrical control while the masking component and all parts of the latter remain fixed in a stationary position, and, secondly, improved optical apparatus employing such masking devices as components thereof for a variety of possible applications. One exemplary application for the invention, for which there is an immediate and substantial need, and with respect to which the invention is hereinafter primarily disclosed for illustration, is in connection with computerized, infrared spectroscopic systems utilizing Hadamard transforms or analogous mathematical techniques for spectral analysis.
b. General Background Prior Art
Conventional devices employed as components in instrumentation for manipulating, analyzing or responding to optical-type radiations include planar mirrors for changing the direction of travel of such radiations, curved mirrors for both collimating or focusing and changing the direction of travel of such radiations, partially "silvered" mirrors for splitting a beam of such radiations into a pair of beams travelling in different directions, lenses for collimating or focusing such radiations, prisms for separating and dispersing such radiations into components corresponding to the wavelengths present in the radiations with the direction of travel of each component being differently displaced, reflective or transmissive diffraction gratings for the same general purpose as prisms and also changing the general direction of travel of the dispersed components when the dispersive element is reflective, various kinds of "photoelectric" sensors for detecting such radiations and responding to the intensity thereof either by producing a corresponding electrical output or a corresponding change in the value of an internal electrical impedance of the sensor, various combinations of the foregoing, etc. Although it is to be understood that apparatus embodying this invention may appropriately employ any of such conventional optical devices as system components, no claim is herein made to any of such components per se.
Another type of device conventionally employed in various types of apparatus for use in connection with optical-type radiations is commonly referred to as a "mask". The purpose of such masks is to permit the passage, by transmission or reflection, of one or more selected cross-sectional portions of such radiations (or one or more mutually displaced wavelength components thereof), while blocking the passage of other portions (or components) of such radiations. A typical mask of the transmission type utilizes one or more apertures or transparent zones in an otherwise opaque plate or the like, and a typical mask of the reflective type utilizes one or more mirrored or reflective zones upon an otherwise transmissive (or opaque and relatively non-reflective) plate or the like. A simple example is the beam restricting "entrance mask" having a single slit in an opaque plate, as commonly employed in many spectrometers. It is also known practice to utilize more than one masking component in succession along the path of travel of optical-type radiations (for example, successive masking components each having a respectively perpendicular, elongate, rectangular aperture or reflective zone may be employed to provide passage for a square cross-sectional portion of such radiations). More recently, the advent of using mathematical techniques such as Hadamard transforms in spectroscopic analysis systems has brought into common usage a type of mask having a plurality of transmissive or reflective zones (typically a number of parallel, rectangular zones spaced from each other in some predetermined arrangement in which they occupy only a portion of the overall area of the mask) for passing a corresponding group of mutually displaced wavelength components of optical-type radiations, the particular group of components passed being dependent upon the precise positioning of such a mask relative to the paths of the radiation components. Again, apparatus embodying this invention may appropriately utilize the foregoing types of conventional masks (for example, as an entrance mask), but no claim is made to any of those general types of masks per se (i.e., apart from the construction thereof with respect to permitting the masking zone pattern to be "altered" under electrical control).